The present invention relates to magnetic tape recording heads, and in particular to a procedure, and structure, for accurately and permanently mounting the same for very precise operation in high-density digital recorder applications of a nature used in computer peripherals, data terminals, and other similar machines.
Magnetic tape heads or pickups are used in conjunction with a wide variety of tape machines, such as audio players/recorders, video players/recorders, tape drive units for computers, and the like. In all such devices it is important that the tape head be properly aligned with the magnetic tape during use to insure error-free interchange. However, tape-to-head alignment becomes most important in digital applications, since here each recorded "bit" is represented by a single upright flux transition on the tape, which may be misread or even skipped if head alignment is not precisely correct. The development of magnetic tape devices for digital data recording applications has led to various arrangements for increasing the number of bits or units of code recorded per inch of tape, to reduce size and cost. Wider tapes are sometimes used to accept multiple tracks of recorded data, thereby obtaining an increased recording density per unit length. Additionally, the "packing density" is continually increased in each recorded track, thus making each flux transition narrower and closer to one another in each track. As a result, the alignment between the magnetic head and the tape has become increasingly more critical, particularly with respect to the acceptable tolerance of the "azimuth angle", which is measured between the vertical axis of the head and any line perpendicular to the axis of motion of a tape sliding thereover. As an example, some installations require that the total accumulated azimuth angle tolerance not exceed .+-.0.degree. 3'.
One known arrangement for aligning a magnetic tape head within a tape machine is illustrated in FIG. 1 of the drawings, wherein a tape head 100 is fixed in a housing portion 101 of the machine by a surrounding "potting" material 102. The tape head 100 is preferably dynamically aligned with the tape by using means such as a master tape which is known to have perfectly-located and aligned pre-recorded bits. That is, the master tape is inserted into the tape player in the read or play mode and an oscilloscope or other similar readout device is connected with the tape machine to indicate when the head 1 has been brought into perfect alignment with the bits on the master tape cartridge. The head 100 is then pivoted within housing 101 until the azimuth angle is within an acceptable tolerance. After the head 100 has been accurately located, it is fixed in position within the housing 101, typically with an epoxy-type of potting material. However, since the potting material shrinks as it hardens, and is not of uniform thickness around the head, the pre-set azimuth angle is inevitably altered as the potting material cures.
Another known arrangement for mounting a magnetic tape head is shown in FIG. 2 of the drawings, wherein tape head 100 is attached to a plate 105. The plate 105 is centrally supported on a rib portion 106 of the housing 101 for pivotal motion thereon. A pair of set screws 107 engage opposite sides of the mounting plate 105, and are adjusted to pivot the plate and tape head 100 into alignment with the master tape passing thereacross, as described hereinabove. After the correct azimuth angle has been achieved, a potting compound is inserted between the plate 105 and the bottom of the housing 101 on both sides of rib 106 to permanently hold the head in place. At best, the dual set screw arrangement of the prior art arrangement shown in FIG. 2 is considered to be somewhat unwieldly to adjust, and it is also inherently inaccurate. Further, by pottong one side of the mounting device at a time, uneven shrinkage of the potting material causes the tape head 100 to move out of the aligned position. This problem is particularly exacerbated when two-part potting compounds are used, as the potting material begins to harden immediately after it is mixed.